In order to calculate the interest for plan Y, let's use the simple interest formula:
[tex]I=P\cdot i\cdot t_{}[/tex]Where I is the interest, P is the principle (initial investment), i is the interest rate and t is the amount of time.
Using P = 1000, i = 0.065 and t = 6, we have:
[tex]I=1000\cdot0.065\cdot6=390[/tex]Now, for plan Z, we use the compound interest formula:
[tex]I+P=P(1+i)^t_{}_{}[/tex]Using now i = 0.06:
[tex]\begin{gathered} I+1000=1000\cdot(1+0.06)^6_{} \\ I+1000=1000\cdot1.06^6 \\ I+1000=1000\cdot1.41852 \\ I+1000=1418.52 \\ I=418.52 \end{gathered}[/tex]So plan Z offer better returns in these conditions.